Patent GB-1152144-A (GB)
Title: Switching Power Amplifier and Servo Apparatus comprising same
Inventor: CITRIN DAVID ARON
IPC: H02M7/5387
Filed: 1967-07-11
Abstract: 1,152,144. Control of D.C. motors. GENERAL ELECTRIC CO. 11 July, 1967 [3 Jan., 1967], No. 31958/67. Heading H2J. [Also in Division H3] A servomotor 11 is supplied with pulsed current from a D.C. source through bridge-connected switches 12-15, each switch comprising parallel-connected power transistors all of which are adapted to be supplied with turn-on signals in accordance with the polarity and magnitude of an error control signal for determining the direction of rotation of the motor and the pulse duration. The power switches, which are connected to circulating diodes 16-19 are controlled by logic circuits 21-24, the circuits 21, 22 being associated with a lock-out circuit 25 for preventing short-circuiting due to simultaneous conduction of the switches 12, 13. Similarly, a lockout circuit 26 is intercoupled between the logic circuits 23, 24, associated with the switches 14, 15. The signals from the circuits 21-24 are supplied through respective phase splitter and driver networks 27-30 which also receive pulses from driver circuit 32 for partially compensation for the saturated voltage-drop of the power switches. The circuit 32 is supplied from square-wave signal generator 33 which also supplies a triangular wave form reference signal generator 34 having its output connected to a power amplifier control circuit 35. The latter also receives the servo error signal which is added to the reference signal to form a composite signal. A threshold circuit 36 supplies bias signals to circuits 22, 24, so that both switches 13, 15 are conductive when there is no error signal. When the composite signal produces a positive switching component which exceeds the threshold value of the circuit 22, the switch 13 is turned-off and the switch 12 is turned-on after a delay caused by the lock-out circuit 25 until the switch 13 is fully off. If the value of the composite signal increases, the pulses applied to the motor are extended. When the composite signal is negative in character, the switch 15 is turned-off and the switch 14 is turned-on by the associated circuits 23, 24. Current feed-back signals are developed across resistors 37, 38, the resistor 37 being used unless the switch 12 is effective in which case the resistor 38 is selected to provide feed-back signals for stabilizing the system. The amplifier 35, Fig. 3 (not shown), comprises transistor (41) which receives signals from the generator 34 and the error signal respectively, two out-of-phase output signals being derived from load resistors (49, 51) connected to the collectors of two further transistors (43, 44). Each of the logic circuits, Fig. 4 (not shown), comprise a first stage transistor (61) which receives the composite signal from the amplifier 35 and has its emitter connected to a bias source. A second stage transistor (62), which is connected as an emitter follower amplifier, inverts and shapes the output of the first transistor as well as providing a signal for selecting the resistor 37 or 38. The signal from the emitter follower is applied to a Darlington pair (64, 65) to drive a differential AND circuit comprising a pair of transistors (66, 67) for deriving a pair of complementary turn-on signals. The driver circuits 27-30, Fig. 7 (not shown), each comprise a pair of switching transistors (91, 92) for recombining the complementary signals and applying the combined signal to the control electrode of the associated power switch (103-105). Each of the switching transistors is connected to a secondary winding of a pulse transformer, the primary windings (95p, 96p) being supplied with pulsed excitation voltages in phase with switching potentials supplied to the differential AND circuits. The voltages developed across the secondary windings (95 SUL, 96 SUL) of the pulse transformer offset the control electrode-emitter saturation voltage of the power switch, Fig. 5 (not shown). The feed-back signals derived from the resistors 37, 38, are passed to non-inverting (111) and inverting amplifiers (113) respectively, and then to a summing amplifier (112). Switching transistors (116, 117) are connected in parallel with the inputs to the summing amplifier and are controlled by the logic circuits for selecting the feed-back signal to be passed to the summing amplifier in accordance with the power switch selected for conduction, Fig. 10 (not shown).